Our objective is a better understanding of mammalian reproduction. By the use of many inbred strains of mice as models, we will catalogue and study the genetically determined variation in reproductive patterns and determine the relative importance of pheromonal and photic stimuli. We will attempt to propagate infertile lines by fertilization in vitro and by egg transfer. We hope to identify the pheromones and their receptors. We will attempt to perfect and simplify the methods for fertilization, egg maturation and embryo culture, all in vitro. We will use these techniques to study embryo metabolism gene expression, sex determination, X-chromosome inactivation, hermaphrodism, and differentiation. We will use these methods to establish clones from blastomeres and so conduct genetic studies without establishing pregnancies. We will continue to produce chimeras to study oncology, immunology, genetics, and behavior. We will use cryobiological methods to freeze, store, and thaw whole embryos and to conduct a pilot study for the establishment of a repository for frozen genetic material.